In the prior art, methods are known for preparing weakly or strongly superalkalinized sulfonates from sulfonic acids obtained by the sulfonation of different alkyl aryl hydrocarbons and from an excess of alkaline earth metal base. These compounds are useful detergents when employed in a lubrication oil composition. The alkyl aryl hydrocarbons subjected to the sulfonation reaction are obtained by alkylation via the Friedel and Craft reaction of different aryl hydrocarbons, particularly aromatics with two different types of olefin; namely, branched olefins and linear olefins. Typically, branched olefins are obtained by the oligo polymerization of propylene to C15 to C42 hydrocarbons, particularly the propylene tetrapolymer dimerized to an average of C24 olefin. The useful linear olefins typically are obtained by the oligo-polymerization of ethylene to C14 to C40 hydrocarbons.
While it is relatively easy to obtain a good dispersion in the medium of alkaline earth base not fixed in the form of salt if the sulfonic acid is derived from a hydrocarbon obtained by alkylation of an aryl hydrocarbon with a branched olefin. It is difficult if the alkylation is effected with a linear olefin. It is particularly difficult for the alkylation of an aryl hydrocarbon where it is monoalkyl and where a high percentage of the alkyl aryl hydrocarbons have the aryl substituent on positions 1 and 2 of the linear alkyl chain due to the formation of a skin in the open air. This poor dispersion is more pronounced if the medium also contains a high proportion of sulfonate, that is if it corresponds, according to ASTM D-2896, to a low base number (BN between 3 and 60), hence to a low content of free lime and the absence of carbon dioxide and carbonate.
In fact, the alkylation reaction between benzene in a large molar excess and another aromatic or aryl hydrocarbons around 25 mole % of the alkyl aryl hydrocarbon has the aryl substituent on positions 1 and 2 of the linear alkyl chain but displays an undesirable characteristic. When prepared by the method described, for example in U.S. Pat. No. 4,764,295, this high proportion alkyl aryl hydrocarbon having an aryl radical on position 1 or 2 of the linear alkyl chain results in a sulfonate that exhibits hygroscopic properties such that as superficial “skin” is formed. This “skin” makes this product unacceptable as an additive for lubricating oil. Furthermore, the formation of the superficial skin is generally accompanied by a very low filtration rate, a high viscosity, a low incorporation of calcium, a deterioration of anti-rust performance, and an undesirable turbid appearance or even sedimentation, when the sulfonate thus prepared is added at the rate of 10% by weight to a standard lubricating oil and stored for examination. Although a high proportion of the aryl substituent on positions 1 and 2 of the linear alkyl chain provides some performance benefits, the formation of the “skin” has limited its application.
To study this phenomenon, the applicant has carried out chromatographic analyses to identify each of the different isomers differing by the position of the aryl radical on the carbon atom of the linear alkyl chain and examined their respective influence on the properties of the corresponding alkyl aryl sulfonates of alkaline earth metals obtained from these different isomers.
In U.S. Pat. No. 5,939,594, the applicant has thus discovered that he could overcome the aforementioned drawbacks in as much as the mole % of the aryl hydrocarbon, other than benzene, having the aryl substituent on position 1 or 2 of the linear alkyl chain was between 0 and 13% and particularly between 5 and 11% and more particularly between 7 and 10%. However, such a process has some drawbacks: for example, benzene could not be used as the aryl hydrocarbon—since it leads to the formation of the skin, and if alkylation was conducted through a HF process, a staggered reaction (two reactors in series) was required. Therefore, if alkylation was conducted through a fixed bed process, two reactors were also required: an isomerization reactor in order to decrease the level of double bound between carbons 1 and 2 down to less than 13% and then a alkylation reactor. Such afore mentioned process has at least two drawbacks: chlorine is utilized and two reactors are required for the alkylation reaction.
In U.S. Pat. No. 6,204,226, the applicant has discovered that he could overcome the aforementioned drawbacks (avoid the necessity of having two reactors at alkylation step and the chlorine) with the use of benzene as aromatic hydrocarbon by employing the following mixture of alkaline earth metals having:
a) from 20% to 70% by weight of a linear mono alkyl phenyl sulfonate in which the linear mono alkyl substituent contains from 14 to 40 carbon atoms, preferably from 20 to 40 carbon atoms, and the mole % of the phenyl sulfonate radical fixed on position 1 or 2 of the linear alkyl chain is between 10% and 25% preferably between 13% and 20% and,
b) from 30% to 80% by weight of a branched mono alkyl phenyl sulfonate in which the branched mono alkyl substituent contains from 14 to 18 carbon atoms.
However, due to the high content of linear mono alkyl phenyl sulfonate substituted in position 1 or 2 of the linear alkyl chain, a large quantity of branched mono alkyl phenyl sulfonate in which the branched mono alkyl substituents contain from 14 to 18 carbon atoms was required to avoid skin formation and moisture sensitivity, but as the average molecular weight and the level of linear mono alkyl phenyl sulfonate having a C14 to C40 linear alkyl chain is too low, some performances such as solubility in a severe formulation and skin formation in the open air after 20 days, decrease.
Similarly, in U.S. Pat. No. 6,054,419 the applicant has discovered that he could overcome the aforementioned drawbacks with the use of benzene as an aromatic hydrocarbon by increasing the level of total linear mono alkyl sulfonate having a C14 to C40 linear chain due to the fact that the molar proportion of the phenyl sulfonate substituent in position 1 or 2 is decreased. From preferably between 10 to 25% to down to 0% to 13%. Through the mixture of alkyl aryl sulfonates of superalkalinized alkaline earth metal comprising:
a) 50 to 85% by weight of a mono phenyl sulfonate with a C14 to C40 linear chain wherein the molar proportion of phenyl sulfonate substituent in position 1 or 2 is between 0 and 13% and,
b) 15 to 50% by weight of heavy alkyl aryl sulfonate, wherein the aryl radical is phenyl or not and the alkyl chain are either two linear alkyl chains with a total number of carbons of 16 to 40 or one or a plurality of branched alkyl chain with on average a total number of carbon atoms of 15 to 48.
In as much as theses mixtures contain less than 10% of linear mono alkyl phenyl sulfonate substituted in position 1 or 2 of the linear alkyl chain, they avoid the “skin” formation and do not display too much sensibility to water. But as the level of total linear mono alkyl phenyl sulfonates (having a C14 to C40 linear alkyl chain) decreases, some performances such thermal stability at 80° C., solubility in severe formulations also correspondingly decreases. Moreover, this application has 2 drawbacks, the use of benzene which is more toxic than toluene or xylene, the necessity of two reactors at alkylation step.
The structure of the alkylates (linear and long alkyl chain) which give a high mole percentage of aryl sulfonate radical in position 1 or 2 of the linear alkyl chain is important for improvement of compatibility, solubility, thermal stability, foaming, dispersion and reduction of sediment in the final package where alkyl aryl sulfonates are mixed with sulfurized overbased alkylphenates. Therefore, there remains a need to develop oil soluble detergent mixture having a high mole percentage or the aryl sulfonate radical in position 1 or 2 or the linear chain, which does not quickly develop an unacceptable skin, mitigates the health issues and improves the solubility and compatibility of the detergent mixture.